Mobile bearing unicompartmental knee

ABSTRACT

An orthopedic knee component for implanting within a single compartment of a human knee includes, in a first embodiment a tibial tray having a superior surface having a plurality of tabs disposed along an exterior edge thereof, a bearing component having a superior surface adapted to articularly engage a femoral knee prosthesis and a circumferential groove disposed therearound with which the tabs of the tibial tray cooperatively engage such that the bearing component is movable relative to the tibial tray. In a second embodiment, an orthopedic knee component for implanting within a single compartment of a human knee includes: a tibial tray in supporting engagement with a bearing component, wherein the bearing component includes a superior surface adapted to articularly engage a femoral knee prosthesis and a pair of slots disposed along the superior surface of the bearing component, the femoral component having a pair of rails extending from the articulating surface thereof such that the rails can slidingly engage the slots, and such that the bearing component is movable relative to the tibial tray.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to prosthetic knee implants ofthe type commonly referred to as “mobile bearing.” More specifically theinvention relates to mobile bearing knees for use in unicompartmental(“uni”) knee prostheses.

2. Description of the Related Art

Prosthetic knee implants having a bearing component that is movablerelative to a fixed tibial tray during flexion and extension of aperson's knee joint are known as mobile bearing knees and will bereferred to as such throughout this document. Mobile bearing kneesgenerally consist of a tibial tray affixed to a prepared proximal tibiaand a bearing component which typically comprises ultra high molecularweight polyethylene (“UHMWPE”). The bearing component is adapted toallow a femoral component to articulate against the same. Often, thereexists a mechanism or a plurality of mechanisms to restrict or limitmovement of the bearing component relative to the tibial componentduring movement of the knee.

It has recently become a goal of physicians to perform orthopedicsurgeries, such as knee arthroplasty, in a less invasive or minimallyinvasive manner. To this end, orthopedic surgeons have begun performinguni knee arthroplasty in situations where only one compartment of apatient's knee is affected by disease or trauma. Partial kneearthroplasty avoids causing trauma to the unaffected compartment of theknee. In addition, uni knee implants are smaller than total kneeimplants. Thus, partial knee arthroplasty is a naturally less invasivealternative to total knee arthroplasty. However, as uni prosthetic kneejoints are less well known than their total knee replacementcounterparts, few, if any, designs exist for mobile bearing uni knees.

SUMMARY OF THE INVENTION

The present invention, in one embodiment thereof, comprises anorthopedic knee component for implanting within a single compartment ofa human knee having a tibial tray that includes a superior surfacehaving a plurality of tabs disposed along an exterior edge thereof, abearing component disposed upon the superior surface of the tibial trayhaving a superior surface adapted to articularly engage a femoral kneeprosthesis and a circumferential groove disposed therearound with whichthe tabs of the tibial tray cooperatively engage such that the bearingcomponent is movable relative to the tibial tray without tipping orleading to dislocation.

The invention, in a another embodiment thereof, comprises an orthopedicknee component for implanting within a single compartment of a humanknee including a tibial tray in supporting engagement with a bearingcomponent, wherein the bearing component includes a pair of slotsdisposed along the superior surface of the bearing component and asuperior surface adapted to articularly engage a femoral kneeprosthesis. The femoral component has a pair of rails extending from thearticulating surface thereof, such that the rails can slidingly engagethe slots and such that the bearing component is movable relative to thetibial tray.

An advantage of the present invention is that it provides a mobilebearing prosthetic knee useful in with a partial knee arthroplasty.Other advantages of the invention will be apparent to those of skill inthe art upon reading the following descriptions and claim and uponviewing the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and objects of this invention,and the manner of obtaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a perspective view of a first embodiment of the presentinvention

FIG. 2 is a side view of the first embodiment of the present invention

FIG. 3 is a perspective view of a tibial tray according to the firstembodiment of the present invention.

FIG. 3 a shows an alternative embodiment of the tibial tray of FIG. 3.

FIG. 4 is a side view of the tibial tray according to a first embodimentof the present invention.

FIG. 5 is a perspective view of a second embodiment of the presentinvention.

FIG. 6 is a side view of the second embodiment of the present invention.

FIG. 7 is a front exploded view of the second embodiment of the presentinvention.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the drawings represent anexemplary embodiment of the present invention, the drawings are notnecessarily to scale and certain features may be exaggerated to betterillustrate and explain the invention. The exemplification set out hereinillustrates an exemplary embodiment of the invention only and suchexemplification

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the following directional definitions apply. Anteriorand posterior mean nearer the front or nearer the back of the bodyrespectively. Thus, for the knee joint described herein, anterior refersto that portion of the knee that is nearer the front of the body, whenthe leg is in an extended position. Proximal and distal mean nearer toor further from the root of the structure, respectively. For example,the distal femur is a part of the knee joint while the proximal femur iscloser to the hip joint. Finally, the adjectives medial and lateral meannearer the median plane or further from the median plane respectfully.The median plane is an imaginary vertical plane through the middle ofthe body that divides the body into right and left halves.

In FIG. 1, there is shown a perspective view of a prosthetic uni kneeimplant 100 according to a first embodiment of the present inventioncomprising: tibial tray 110 and bearing component 160. Implant 100 isinsertable into the joint space within a single compartment of a humanknee in order to replace bone and tissue lost to trauma or disease. Itis to be appreciated that an embodiment of the present invention isuseful for medial partial knee arthroplasty, lateral partial kneearthroplasty, or total knee arthroplasty.

Referring now to FIG. 3, tibial tray 110 of the present inventioncomprises: a superior surface 120, at least two tabs 130, and inferiorsurface 140, and pegs 150 for attaching tray 110 to a human tibia.Tibial tray 110 is appropriately sized to fit within the joint spacecreated during a knee arthroplasty. Tibial tray 110 may further compriseany biocompatible material having the requisite mechanical propertiesnecessary for tray 110 to function as a tibial implant, includingmetals, plastics, and ceramics. Generally, however, tibial tray 110comprises a biocompatible metal such as titanium or cobalt alloy.

Referring again to FIG. 3, superior surface 120 is generally flat andsmooth; it is adapted to allow bearing component 160 (describedsubsequently herein) to slidingly engage the same. Tibial tray 110further comprises at least two tabs 130 disposed along the exterior edgeof superior surface 120. Each tab 130 comprises a substantially “L”shape such that each tab comprises a first tab portion 131 connected toand extending superiorly from superior surface 120 of tray 110. Each tab130 further comprises a second tab portion 132 that is connected to thefree end of first tab portion 131 and that extends therefrom generallytoward the interior of superior surface 120, such that second tabportion is generally parallel to superior surface 120.

Referring still to FIG. 3, Tibial tray 110 further comprises inferiorsurface 140. Inferior surface 140 comprises means 150 for fixedlyattaching tibial tray 110 to a surgically prepared proximal tibia. Means150 may comprise any means known in the art for attaching a tibial trayto a proximal tibia. However, the exact means 150 of attaching tibialtray 110 to a proximal femur are not important to the present invention.For example, means 150 may comprise pegs, screws, pins, a bone ingrowthsurface, an elongated stem for insertion into the intramedullary canalof a tibia, or a combination of these features.

Referring back to FIG. 1, prosthetic knee implant 100 further comprisesbearing component 160. Bearing component 160 generally comprises athermoplastic or thermoset polymer material such as ultra high molecularweight polyethylene (“UHMWWPE”) or highly cross-linked UHMWPE. Bearingcomponent 160 further comprises a shape and size suitable for use as abearing component in a uni prosthetic knee.

Bearing component 160 further comprises a superior surface 170 adaptedto accommodate the rotational and translational articulation of a distalfemur uni prosthesis. The exact shape of superior surface 170 or theexact design of such distal femoral implant, however, is not critical tothis embodiment of the present invention.

Bearing component 160 also comprises inferior surface 180 shaped toslidingly engage superior surface 120 of tibial tray 110 such thatbearing component 160 can move relative to tray 110. In the embodimentshown in FIGS. 1-4, surface 120 of tray 110 is flat, and bearingcomponent 160 is movable in any direction in a plane that is generallyparallel to surface 120.

Bearing component 160 further comprises a generally verticalcircumferential wall having groove 190 disposed thereon. Groove 190 ishas a depth and height suitable to allow any second tab portion 132 tofit therein. The depth and height of groove 190 are such that whensecond tab portion 132 of tabs 130 fit into groove 190 there is a gapremaining within the height of groove 190, such that bearing component160 may easily slide along superior surface 120 of tibial tray 110. Tabs130 prevent bearing component 160 from sliding off of superior surface120 of tibial tray 110. It is desirable for at least one of tabs 130 toengage groove 190 in order to prevent bearing component 160 fromtipping.

FIGS. 5-7 show implant 200 according to a second embodiment of thepresent invention, wherein the implant comprises femoral component 210,bearing component 260 and tibial tray 290.

Referring now to FIG. 5, specifically femoral component 210 comprises abone contacting surface 220 for engaging a surgically prepared distalfemur. Bone contacting surface 220 generally includes a plurality ofintersecting planes and means of affixing femoral component 210 to theprepared distal femur. These means may include press fitting, screws,bone ingrowth materials, posts or a combination of the same.

Referring now to FIGS. 5 and 6, femoral component 210 further comprisesarticulating surface 230 disposed opposite bone contacting surface 220.Articulating surface 230 is generally arcuated such that is can rotateand translate relative to a bearing component, such as the one describedherein below.

Referring now to FIG. 7, femoral component 210 further comprises medialand lateral edges and a rail 250 disposed along each edge and extendingfrom articulating surface 230. Rails 250 are adapted to slidingly engageslots 275 of bearing component 260 described below.

Continuing to refer to FIGS. 5 and 7, there is shown bearing component260. Bearing component 260 comprises a shape and size suitable for useas a bearing component in a uni prosthetic knee.

Bearing component 260 further comprises a superior surface 270 adaptedto accommodate the rotational and translational articulation of thefemoral component. Slots 275, disposed along the medial and lateraledges of surface 270, are adapted to slidingly receive rails 250 orfemoral component 210 such that femoral component 210 cannot movetransversely relative to bearing component 260.

It is to be understood, however, that a variety of slot and railsconfigurations would be within the scope of the present invention. Byway of example, but not limitation, the invention could comprise lessthan or more than two rail and slot combinations. Alternatively, therails could be disposed on the superior surface 270 of bearing component260 and the slots could be disposed on the articulating surface 230 offemoral component 210.

Bearing component 260 also comprises inferior surface 280 shaped toslidingly engage superior surface 291 of tibial tray 290 such thatbearing component 280 can move relative to tray 290. In the embodimentshown in FIGS. 5-7, surface 291 of tray 290 is flat, and bearingcomponent 260 is movable in any direction in a plane that is parallel tosurface 291.

It will be appreciated by those skilled in the art that the foregoing isa description of a preferred embodiment of the present invention andthat variations in design and construction may be made to the preferredembodiment without departing from the scope of the invention as definedby the appended claims.

1. A mobile bearing unicondylar knee implant for implanting within a single compartment of a human knee joint and adapted to cooperate with a prosthetic femoral component, the implant comprising: a bearing component, the bearing component having a superior surface adapted to allow articulation of the prosthetic femoral component thereon, an inferior surface adapted to slidingly engage a superior surface of a tibial tray, and an exterior wall having a groove disposed therearound; and a tibial tray having a superior surface having at least two tabs disposed along an edge thereof, the tabs having a first tab portion extending proximally from the superior surface of the tibial tray and a second tab portion attached to the first tab portion extending generally toward the center of the tibial tray such that the tabs are selectively engageable within the groove, wherein the bearing component freely moves in any direction in a plane that is generally parallel to said superior surface of said tibial tray while cooperation of said groove and said at least two tabs prevents said bearing component from sliding off the edge of said superior surface of said tibial tray.
 2. The implant of claim 1, wherein the bearing component comprises a material selected from the group consisting of polyethylene, ultra high molecular weight polyethylene, and cross-linked ultra high molecular weight polyethylene.
 3. The implant of claim 1, wherein the tibial tray further comprises an inferior surface having bone ingrowth means.
 4. The implant of claim 3, wherein the inferior surface of the tibial tray comprises a material selected form the group consisting of porous titanium, porous tantalum.
 5. The implant of claim 1, wherein the number of tabs is selected from the group consisting of 2 and
 4. 